Wastewater disposal tied to surge in Oklahoma earthquakes

Jul. 3, 2014
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Chad Devereaux examines bricks that fell from three sides of his in-laws' home in Sparks, Okla., in 2011, following two earthquakes that hit the area in less than 24 hours. New research suggests the rise in quake activity in Oklahoma may be tied to deepwater injection wells. / Sue Ogrocki, AP

by Hoai-Tran Bui, USATODAY

by Hoai-Tran Bui, USATODAY

In 2014, it was not California that had the highest number of earthquakes over the magnitude of 3. It was Oklahoma.

Researchers say the rise in earthquakes may be a byproduct of wastewater disposal from oil and gas drilling operations. A study released Thursday in the journal Science found that the injection of subsurface wastewater from these operations into disposal wells is linked to the dramatic rise of earthquakes in central Oklahoma since 2009.

"It's been a real puzzle how low seismic activity level can suddenly explode to make (Oklahoma) more active than California," says Katie Keranen, a geophysics professor at Cornell University and lead researcher of this study.

The research merged seismic data from 2008 to 2013 with the locations of disposal wells in the state using the database from the Oklahoma Corporation Commission, which regulates public service corporations. The team found that many of the earthquakes occur in areas where thousands of barrels of wastewater are being injected into relatively few disposal wells.

"Wastewater is using the same well for months and years, leading to an accumulative pressure," Keranen says. "Because we have such high volumes (of wastewater) going in, the rocks are quite permeable, and the pressure is able to propagate to really far distances. If the fault is ready to fail, it doesn't take a lot of change in pressure to trigger an earthquake."

Pumping water into the earth does two things, says Columbia University seismologist and study co-author Geoff Abers. It adds weight to the ground so that the crust pushes downward, and it increases fluid pressure in the cracks along the faults, which are fractures along the crust of the Earth. This reduces the strengths of those faults and their ability to withstand friction. Without friction holding the crusts in place, those faults are more susceptible to earthquakes.

High volumes of wastewater are injected into a small fraction of the wells - the research team found that 89 disposal wells out of about 10,000 were the biggest offenders. But the pressure in those high-volume wells helped produce earthquakes over a large area, Abers says. Many of the earthquakes were up to 20 miles away from where the fluids were injected.

"The big thing for our study is these really high-volume injection operations seem to have the greatest risk of earthquakes," Abers says.

Almost none of these earthquakes were tied to hydraulic fracturing, commonly called fracking, the researchers say. With hydraulic fracturing, the pressure is high but tightly controlled, and only for a short period of time, whereas disposal wells put high pressure on the crusts day after day, Keranen says.

Wastewater is produced during the process of hydraulic fracturing, where water, sand and chemicals are pumped into the ground to break up the rocks and release gas and oil.

But the Oklahoma Independent Petroleum Association's president, Mike Terry, released a statement on the study, saying in part the water is not a product of hydraulic fracturing. Keranen's report says the large disposal wells tied to the seismic activity are part of "dewatering plays." That's a reference to an enhanced process for oil recovery called dewatering where oil from older oil wells is often mixed with water from ancient sea beds where the oil was deposited initially. That water is removed from the oil and then returned to the injection wells. Still, Terry called dewatering a "minute" part of Oklahoma's oil and natural gas development.

"The OIPA and the oil and gas industry as a whole support the continued study of Oklahoma's increased seismic activity, but a rush to judgment based on one researcher's findings provides no clear understanding of the causes," Terry said.

Terry points out that there has been "increased seismic activity (across) North America, including Idaho, Virginia, Arizona and northern Mexico, where dewatering projects and unconventional oil and gas development are non-existent."

The rise in seismic activity in Oklahoma is part of a surge in earthquakes in midcontinent America, with more earthquakes occurring in Arkansas, Colorado, Ohio and Kansas, according to William Ellsworth, a seismologist at the U.S. Geological Survey, a scientific research organization. Ellsworth, who has done previous studies on injection-induced earthquakes, says the idea that changes in pressure underground are caused by pumping fluids into the earth has been understood for about half a century, but research is still being done to draw the connection.

"Since 2009, we've seen a great increase in earthquake activity in the midcontinent," Ellsworth says. "We don't know (if wastewater injection) is the only explanation, but I think the rate of activity is so high, particularly in Oklahoma, that there are no viable other factors."

Wastewater is difficult to treat because it consists of ancient ocean water that was residing under the surface, in addition to the chemicals and water and sand mixture that were originally pumped down, so injection into the deep disposal wells is often the best option, Ellsworth says.

"Injecting (wastewater) into earth under controlled conditions is perfectly reasonable, as long as it's managed correctly," he says. "The challenge for regulators is to understand how new scientific understanding can lead to better regulations."

Keranen says the 10,000 injection wells they reviewed in Oklahoma were all within regulation, and they hope the study will guide oil and gas companies to monitor the wastewater injection.

"The next step is on the (regulators) who think about the trade-offs of earthquake public safety and oil (production)," Abers says.